Prior art methods for detecting hepatitis B core antigen (HBcAg) involved the use of immune adherence hemagglutination assay (IAHA) or complement fixation (CF) assay. A disadvantage of such assays is that the end-point determination requires interpretation of observed results and therefore is necessarily subjective to some degree. These assays are not sufficiently sensitive for routine use to detect the presence of HBcAg in biological fluids, expecially sera or plasma, in order to prevent transmission of hepatitis B disease by transfusion and also to diagnose the presence of this disease in a person.